#include <iostream>
#include <vector>
#include <queue>
#include <limits>
using namespace std;
const int INF = 1e9;
struct Edge {
int to, cost;
};
int main() {
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int K, N, M, O;
cin >> K >> N >> M >> O;
vector<vector<Edge>> graph(N);
for (int i = 0; i < M; ++i) {
int a, b, t;
cin >> a >> b >> t;
if (b / K == (a / K) + 1) {
graph[a].push_back({b, t});
}
}
for (int i = 0; i < O; ++i) {
int start, end;
cin >> start >> end;
vector<int> dist(N, INF);
dist[start] = 0;
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<>> pq;
pq.push({0, start});
while (!pq.empty()) {
auto [d, u] = pq.top(); pq.pop();
if (d > dist[u]) continue;
for (const Edge& e : graph[u]) {
if (dist[e.to] > dist[u] + e.cost) {
dist[e.to] = dist[u] + e.cost;
pq.push({dist[e.to], e.to});
}
}
}
if (dist[end] == INF)
cout << -1 << endl;
else
cout << dist[end] << endl;
}
return 0;
}
